Clutched steam turbine low pressure sections and methods therefore

ABSTRACT

Solutions for clutching steam turbine low pressure sections are disclosed. In one embodiment, a system includes: a first low pressure steam turbine including a first shaft; a second low pressure steam turbine including a second shaft; a clutch for coupling and uncoupling the first shaft and the second shaft; a conduit for delivering a working fluid to the first low pressure steam turbine and the second low pressure steam turbine; a valve within the conduit, the valve having an open position and a closed position, the closed position preventing flow of the working fluid to the second low pressure steam turbine; and a controller for operating the clutch and the valve, the controller uncoupling the second shaft from the first shaft and closing the valve in response to the first and second low pressure steam turbine attaining a predetermined low part load.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to solutions for clutchingsteam turbine low pressure sections. Specifically, the subject matterdisclosed herein relates to using a clutch-valve mechanism to engage anddisengage low pressure sections of a steam turbine power generationsystem.

Steam turbine power systems are designed and built with particular loadconditions in mind. Often, these systems are built to handle the peak ornear-peak loads of their customers, which may coincide with afternoonhours where the ambient temperature is high (e.g., above 27 degreesCelsius). However, during periods of lower demand, these systems mustrun at off-peak loads. For example, a steam turbine power system mayreduce its output to well below fifty percent of its rated power duringthe evening hours (e.g., after 9:00 pm local time), when customersrequire very little electricity. Reducing the output of the steamturbine power system to such levels may cause, among other things,mechanical damage to the steam turbine's components, resulting in morefrequent parts replacement and increased costs.

BRIEF DESCRIPTION OF THE INVENTION

Solutions for clutching steam turbine low pressure sections aredisclosed. In one embodiment, a system includes: a first low pressuresteam turbine including a first shaft; a second low pressure steamturbine including a second shaft; a clutch for coupling and uncouplingthe first shaft and the second shaft; a conduit for delivering a workingfluid to the first low pressure steam turbine and the second lowpressure steam turbine; a valve within the conduit, the valve having anopen position and a closed position, the closed position preventing flowof the working fluid to the second low pressure steam turbine; and acontroller for operating the clutch and the valve, the controlleruncoupling the second shaft from the first shaft and closing the valvein response to the first and second low pressure steam turbine attaininga predetermined low part load.

A first aspect of the invention provides a steam turbine systemcomprising: a first low pressure steam turbine including a first shaft;a second low pressure steam turbine including a second shaft; a clutchfor coupling and uncoupling the first shaft and the second shaft; aconduit for delivering a working fluid to the first low pressure steamturbine and the second low pressure steam turbine; a valve within theconduit, the valve having an open position and a closed position, theclosed position preventing flow of the working fluid to the second lowpressure steam turbine; and a controller for operating the clutch andthe valve, the controller uncoupling the second shaft from the firstshaft and closing the valve in response to the first and second lowpressure steam turbine attaining a predetermined low part load.

A second aspect of the invention provides a combined cycle power plantsystem comprising: a gas turbine operably connected to a firstgenerator; a steam turbine section operably connected to the gasturbine; and a steam turbine system operably connected to the steamturbine section, the steam turbine system including: a first lowpressure steam turbine including a first shaft; a second low pressuresteam turbine including a second shaft; a clutch for coupling anduncoupling the first shaft and the second shaft; a conduit fordelivering a working fluid to the first low pressure steam turbine andthe second low pressure steam turbine; a valve within the conduit, thevalve having an open position and a closed position, the closed positionpreventing flow of the working fluid to the second low pressure steamturbine; and a controller for operating the clutch and the valve, thecontroller uncoupling the second shaft from the first shaft and closingthe valve in response to the first and second low pressure steam turbineattaining a predetermined low part load.

A third aspect of the invention provides a method of operating a steamturbine system, the method comprising: uncoupling a second low pressuresteam turbine from a first low pressure steam turbine using a clutch,the uncoupling being in response to the first and second low pressuresteam turbine attaining a predetermined low part load.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will be more readilyunderstood from the following detailed description of the variousaspects of the invention taken in conjunction with the accompanyingdrawings that depict various embodiments of the invention, in which:

FIG. 1 shows a schematic block diagram illustrating a steam turbinesystem including clutched steam turbine low pressure sections accordingto embodiments of the invention.

FIG. 2 shows a schematic block diagram illustrating portions of acombined cycle power plant system according to embodiments of theinvention.

FIG. 3 shows a steam turbine exhaust loss curve illustrating performancecharacteristics of clutched steam turbine low pressure sectionsaccording to embodiments of the invention.

It is noted that the drawings of the invention are not to scale. Thedrawings are intended to depict only typical aspects of the invention,and therefore should not be considered as limiting the scope of theinvention. In the drawings, like numbering represents like elementsbetween the drawings.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, aspects of the invention provide for clutched steamturbine low pressure sections. As used herein, unless otherwise noted,the term “set” means one or more (i.e., at least one) and the phrase“any solution” means any now known or later developed solution.

As is known in the art of steam turbine power systems, the terms “ratedpower” and “rated mass flow” refer to the total power output and totalmass flow, respectively, of one or more devices under certain predefinedconditions. Typically, the rated power/mass flow of a steam turbinesystem is designed for a particular set of conditions, and thesedesigned conditions are set as the 100 percent rated power/mass flowmarks. When operating at conditions other than design conditions, thepower and mass flow of a steam turbine system may deviate from the 100percent rated power/mass flow mark. Operating conditions below the 100percent rated power/mass flow mark may fall into a few categories. Onesuch category, known as “low part load,” is characterized by running asteam turbine at or under approximately 25% of its rated power/massflow. Low part load is a distinct subset of the broad category known as“part load,” which is characterized by running a steam turbine at lessthan 100% of its rated power/mass flow. As used herein, “low part load”refers to a range of loads that may be approximately 5-25% of a ratedpower/mass flow of a steam turbine system. Low part load conditions mayoccur at different percentages of rated power/mass flow depending upon aplurality of steam turbine conditions. For example, these conditions mayinclude: the low pressure turbine geometry (e.g., last-stage bucketlength), operating conditions (e.g., condenser pressure, temperatures,etc.), operation planning/history (e.g., planned duration of low partloading, previous frequency/duration of low part loading) andmaintenance schedules.

Operating a steam turbine system at its low part load may causeaccelerated mechanical damage to either or both of a first low pressuresteam turbine and a second low pressure steam turbine. In particular,operating low pressure steam turbines at low part loads can causecomplications such as windage overheating, aerodynamic flow separation,flow instability, etc. These complications may result in acceleratedmechanical damage to low pressure section buckets, shafts, rotors,seals, etc. These complications and the mechanical damages they causemay result in costly steam turbine maintenance, stoppages, catastrophicdamage, reduced steam turbine reliability and availability, etc.

While one alternative to running a steam turbine system at low part loadis to completely shut down the system, this may cause a variety of otherproblems. For example, every time a steam turbine power system is shutdown, it may not restart as planned, resulting in additional maintenancecosts and/or missed power generation opportunities. Even further, thecycle of shutting down and restarting the steam turbine power systemcauses wear on plant components such as boilers, heat recovery steamgenerators (HRSGs), conduits/pipes, etc. and system components such asshafts, last stage buckets, rotors, etc. In order to avoid theaforementioned undesirable consequences, clutched steam turbine lowpressure sections are disclosed.

While clutched steam turbine sections have been used in the past, theyhave aimed at improving the efficiency of steam turbine power generationsystems by reducing the exhaust loss of each individual steam turbine.These prior clutched steam turbine sections have attempted to improveefficiency by disengaging one low pressure steam turbine from the systemwhen the steam turbine system runs at approximately 50 percent of itsrated power (operating at “part load”). While this approach producesdecreased exhaust losses and an increased annulus velocity, it does notaddress the problems associated with running a steam turbine system atlow part load. In particular, the prior approach does not attempt toreduce the mechanical damage inflicted on steam turbine components dueto running at low part loads. Further, the prior approach does notattempt to reduce the need for a shut-down and subsequent restart of thesteam turbine system during times of low part load.

Turning to the drawings, FIG. 1 shows a schematic block diagram of asteam turbine system 100 according to one embodiment of the invention.Arrows are shown depicting the flow of a working fluid betweencomponents of steam turbine system 100. The term “working fluid” mayrefer to any fluid capable of performing the functions described herein.

Steam turbine system 100 may include a first low pressure steam turbine120 including a first shaft 175, along with a second low pressure steamturbine 130 including a second shaft 185. Steam turbine system 100 mayalso include a clutch 140 for coupling and uncoupling first shaft 175and second shaft 185. Clutch 140 may function as a mechanical linkagebetween first shaft 175 and second shaft 185 during operation of steamturbine system 100. This linkage may allow first shaft 175 and secondshaft 185 to rotate at approximately the same rate of speed. However,under certain operating conditions, clutch 140 may uncouple second lowpressure steam turbine 130 from first low pressure steam turbine 120 bydisengaging second shaft 185 from first shaft 175. Steam turbine system100 may further include a conduit 160 for delivering a working fluid(numbering omitted) to first low pressure steam turbine 120 and secondlow pressure steam turbine 130. Conduit 160 may be, for example, a ductor a pipe made in part from metal, composite, or a polymer. Alsoincluded in steam turbine system 100 may be a valve 150 located withinconduit 160. Valve 150 may have an open position and a closed position,where the closed position prevents flow of the working fluid to secondlow pressure steam turbine 130. Valve 150 may be, for example, a two-wayvalve. As is known in the art of fluid mechanics, a two-way valve eitherprevents a portion of the flow of a working fluid through a pathway, orit allows a portion of that flow to pass. Valve 150 may primarilyfunction either in a closed position (total obstruction) or openposition (no obstruction), however, valve 150 may also function in apartially open position (partial obstruction). Valve 150, may, forexample, be a gate valve, a butterfly valve, a globe valve, etc.

Steam turbine system 100 may further include a controller 145 foroperating clutch 140 and valve 150. Controller 145 may be mechanicallyand/or electrically connected to clutch 140 and valve 150 such thatcontroller 145 may actuate clutch 140 and/or valve 150. Controller 145may instruct clutch 140 to uncouple second shaft 185 from first shaft175 and/or may instruct valve 150 to close in response to the first lowpressure steam turbine 120 and second low pressure steam turbine 130attaining a predetermined low part load. Controller 145 may be acomputerized, mechanical, or electromechanical device capable ofactuating valve 150 and engaging/disengaging clutch 140. In oneembodiment, controller 145 may be a computerized device capable ofproviding operating instructions to valve 150 and/or clutch 140. In thiscase, controller 145 may monitor the load of steam turbine system 100(via monitoring flow rates, temperature, pressure, and working fluidparameters), and provide operating instructions to valve 150 and/orclutch 140. For example, controller 145 may send operating instructionsto close valve 150 and disengage clutch 140 under certain operatingconditions (e.g., low part load). In this embodiment, valve 150 andclutch 140 may each include electromechanical components, capable ofreceiving operating instructions (electrical signals) from controller145 and producing mechanical motion (e.g., closing of valve, uncouplingof shafts). In another embodiment, controller 145 may be a mechanicaldevice, capable of use by an operator. In this case, the operator mayphysically manipulate controller 145 (e.g., by pulling a lever), whichmay actuate valve 150 and/or clutch 140. For example, the lever ofcontroller 145 may be mechanically linked to valve 150 and clutch 140,such that pulling the lever causes valve 150 and/or clutch 140 to fullyactuate (e.g., by sealing off conduit 160 between first and second lowpressure steam turbines 120, 130 and/or disengaging second shaft 185).In another embodiment, controller 145 may be an electromechanicaldevice, capable of electrically monitoring (e.g., with sensors)parameters indicating that steam turbine system 100 is running at a lowpart load, and mechanically actuating valve 150 and/or clutch 140. Whiledescribed in several embodiments herein, controller 145 may operatevalve 150 and/or clutch 140 through any conventional means.

In any case, when controller 145 uncouples second shaft 185 from firstshaft 175 and closes valve 150 (preventing working fluid flow), secondlow pressure steam turbine 130 is effectively taken “off-line.” Thisallows substantially all of the working fluid to flow through first lowpressure steam turbine 120, causing increased efficiency in first lowpressure steam turbine 120 (shown and described with reference to FIG.3). This further allows for reduced mechanical damage to both second lowpressure steam turbine 130 and first low pressure steam turbine 120.Additionally, first low pressure steam turbine 120 may continueoperating even during low loading conditions. This may provide theadditional benefit of allowing steam turbine system 100 to operatecontinuously without a shut-down and restart.

Also shown in FIG. 1 is a steam turbine section 110, which is coupled tofirst low pressure steam turbine 120 by first shaft 175, and operablyconnected to first low pressure steam turbine 120 and second lowpressure steam turbine 130 via conduit 160. Steam turbine section 110may, for example, be an intermediate pressure steam turbine, a highpressure steam turbine, or may include both high pressure andintermediate pressure sections. In any case, steam turbine section 110may provide working fluid (steam exhaust) to one or both of first lowpressure steam turbine 120 and second low pressure steam turbine 130.Further shown in FIG. 1 is a generator 210, coupled to first lowpressure steam turbine 120 and steam turbine section 110. In oneembodiment, generator 210 may be coupled to first low pressure steamturbine 120 by first shaft 175. Generator 210 may be any standardgenerator capable of converting mechanical energy (rotation of firstshaft 175) into electrical energy. It is understood that while generator210 and steam turbine section 110 are shown as coupled to first lowpressure steam turbine 120 by first shaft 175, generator 210 and steamturbine section 110 may be coupled to second shaft 185 when clutch 140is engaged. However, in conditions of low part load, second low pressuresteam turbine 130 does not provide mechanical energy to generator 210.

FIG. 1 further shows a first condenser 170 operably connected to firstlow pressure steam turbine 120, and a second condenser 180 operablyconnected to second low pressure steam turbine 130. First condenser 170and second condenser 180 may be conventional condensers which cool theworking fluid exiting first low pressure steam turbine 120 and secondlow pressure steam turbine 130, respectively.

FIG. 2 shows portions of a combined cycle power plant system 200according to embodiments of the invention. FIG. 2 includes manycomponents shown and described with reference to steam turbine system100 of FIG. 1. However, combined cycle power plant system 200 mayadditionally include a gas turbine 300, a first generator 310, and aheat exchanger 400 (additional items shown in dashed box “A”). Gasturbine 300 may be operably connected to first generator 310. Gasturbine 300 may be a conventional gas turbine that generates mechanicalenergy via the flow of combustion gas through a turbine (components notshown). First generator 310 may be a conventional generator, capable ofconverting the mechanical energy of gas turbine 300 into electricalenergy. First generator 310 may be coupled to gas turbine 300 via athird shaft 275. Further shown in FIG. 2 is heat exchanger 400 operablyconnected to gas turbine 300 and steam turbine section 110. While heatexchanger 400 is shown as being operably connected to gas turbine 300and steam turbine section 110, it is understood that heat exchanger 400may further be operably connected to one or more of conduit 160, firstlow pressure steam turbine 120 and second low pressure steam turbine130.

Heat exchanger 400 may supply steam to steam turbine section 110, firstlow pressure steam turbine 120, and/or second low pressure steam turbine130, via a conventional conduit, such as those described herein(numbering omitted). Heat exchanger 400 may be a conventional heatrecovery steam generator (HRSG), such as those used in a conventionalcombined-cycle power station. As is known in the art of powergeneration, heat recovery steam generators may use hot exhaust from gasturbine 300, combined with a water supply, to create steam. This steammay then flow to steam turbine section 110, first low pressure steamturbine 120, and/or second low pressure steam turbine 130 via a conduit(e.g., conduit 160).

It is understood that while steam turbine system 100 and combined cyclepower plant system 200 are shown and described herein as including twolow pressure steam turbines (first 120 and second 130), additional lowpressure steam turbines may be included as well. For example, in nuclearor fossil power plants, a third low pressure steam turbine may becoupled to second low pressure steam turbine 130 via shaft 185 or anadditional shaft (not shown). In the case where the third low pressuresteam turbine shares shaft 185 with second low pressure steam turbine130, both second (130) and third low pressure steam turbine may be taken“off-line” from first low pressure steam turbine 120. Where anadditional shaft is used, the third low pressure steam turbine may betaken “off-line” from second low pressure steam turbine 130. In thiscase, a second clutch and second valve may couple and operably connectthe third low pressure steam turbine to second low pressure steamturbine 130, respectively. Controller 145 may control the second clutchand second valve similarly to clutch 140 and valve 150. However, asecond controller may be used to control the second clutch and thesecond valve. This second controller may function substantiallysimilarly to first controller, and may take any form of controllerdescribed herein.

It is further understood that while combined cycle power plant system200 depicts gas turbine 300 on a different shaft (second shaft 275) thansteam turbine section 110 and first low pressure steam turbine 120,these components may all be located on the same shaft (first shaft 175).This configuration is known in the art as a “single-shaft” system. Incontrast, FIG. 2 depicts combined cycle power plant system 200 as a“multi-shaft” system. It is understood that clutched steam turbinesections described herein may be used in either a single-shaft system ora multi-shaft system. In a single-shaft configuration, it is understoodthat gas turbine 400, steam turbine section 110, and first low pressuresteam turbine 120 may all be operably connected to first shaft 175. Inthis case, generator 210 may be the only generator operably connected tofirst shaft 175. In any case, the locations of generator 210, steamturbine section 110 and first low pressure steam turbine 120 on firstshaft 175 may be interchanged. For example, in one embodiment, generator210 may be located between gas turbine 300 and steam turbine section 110on first shaft 175.

While FIG. 2 depicts combined cycle power plant system 200 including asingle gas turbine 300 and a single heat exchanger 400, it is understoodthat additional gas turbines, heat exchangers, and generators may beemployed. For example, additional sets of components shown in phantombox A may be operably connected to, for example, steam turbine section110. In this case, steam turbine section 110 may receive steam inputsfrom a plurality of heat exchangers, resulting in a greater mass flowthrough steam turbine section 110. Accordingly, steam turbine section110 must be large enough to process the increased mass flow. This alsomeans that first low pressure steam turbine 120 and second low pressuresteam turbine 130 must be large enough to process their respectiveshares of the increased mass flow. However, where first low pressuresteam turbine 120 and second low pressure steam turbine 130 are largeenough to process increased mass flow, even greater mechanical damagemay occur during times of low part load. For example, during operationof combined cycle power plant system 200 using a plurality of gasturbines, a decrease in demand for power may cause an operator to shutdown one or more of the gas turbines. Where this shutdown causescombined cycle power plant system 200 to run at low part load, it mayresult in mechanical damage to components of first low pressure steamturbine 120 and/or second low pressure steam turbine 130. In such acase, clutched steam turbine sections may provide even greaterassistance in reducing mechanical damage within components of combinedcycle power plant system 200 than in steam turbine system 100.

Turning to FIG. 3, a steam turbine exhaust loss curve illustratingreduced mechanical damage to steam turbine system 100 is shown. Thisexhaust curve is well known in the art of steam turbine power systems,and illustrates the thermodynamic optimum point (characterized byminimal dry exhaust loss), at which a steam turbine system is mostefficient. Point “A” depicts the performance of steam turbine system 100at low part load before uncoupling of second shaft 185 (second lowpressure steam turbine 130) from first shaft 175 (first low pressuresteam turbine 120). As shown, steam turbine system 100 is far fromrunning at its thermodynamic optimum at point A. However, as explainedherein, clutched steam turbine sections may reduce mechanical damage tocomponents of steam turbine system 100 by increasing mass flow of theworking fluid through first low pressure steam turbine 120. Point “B”depicts steam turbine system 100 after uncoupling of second shaft 185from first shaft 175. While steam turbine system 100 is still running atlow part load at both point A and point B, the mechanical damage to itscomponents may be reduced by taking second low pressure steam turbine130 “off-line” (uncoupling second shaft 185 and first shaft 175).

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A steam turbine system comprising: a first low pressure steam turbineincluding a first shaft; a second low pressure steam turbine including asecond shaft; a clutch for coupling and uncoupling the first shaft andthe second shaft; a conduit for delivering a working fluid to the firstlow pressure steam turbine and the second low pressure steam turbine; avalve within the conduit, the valve having an open position and a closedposition, the closed position preventing flow of the working fluid tothe second low pressure steam turbine; and a controller for operatingthe clutch and the valve, the controller uncoupling the second shaftfrom the first shaft via the clutch and closing the valve in response tothe first and second low pressure steam turbine attaining apredetermined low part load.
 2. The steam turbine system of claim 1,further comprising a steam turbine section coupled to the first lowpressure steam turbine by the first shaft.
 3. The steam turbine systemof claim 2, further comprising a generator coupled to the first lowpressure steam turbine and the second low pressure steam turbine.
 4. Thesteam turbine system of claim 3, further comprising a first condenseroperably connected to the first low pressure steam turbine.
 5. The steamturbine system of claim 4, further comprising a second condenseroperably connected to the second low pressure steam turbine.
 6. Thesteam turbine system of claim 1, wherein the controller includes anelectro-mechanical device.
 7. A combined cycle power plant systemcomprising: a gas turbine operably connected to a first generator; aheat exchanger operably connected to the gas turbine; a steam turbinesection operably connected to the heat exchanger; and a steam turbinesystem operably connected to the steam turbine section, the steamturbine system including: a first low pressure steam turbine including afirst shaft; a second low pressure steam turbine including a secondshaft; a clutch for coupling and uncoupling the first shaft and thesecond shaft; a conduit for delivering a working fluid to the first lowpressure steam turbine and the second low pressure steam turbine; avalve within the conduit, the valve having an open position and a closedposition, the closed position preventing flow of the working fluid tothe second low pressure steam turbine; and a controller for operatingthe clutch and the valve, the controller uncoupling the second shaftfrom the first shaft via the clutch and closing the valve in response tothe first and second low pressure steam turbine attaining apredetermined low part load.
 8. The combined cycle power plant system ofclaim 7, further comprising a second generator operably connected to thesteam turbine system.
 9. The combined cycle power plant system of claim8, wherein the second generator is coupled to the first low pressuresteam turbine.
 10. The combined cycle power plant system of claim 7,further comprising a first condenser operably connected to the first lowpressure steam turbine.
 11. The steam turbine system of claim 10,further comprising a second condenser operably connected to the secondlow pressure steam turbine.
 12. The steam turbine system of claim 7,wherein the controller includes an electro-mechanical device.
 13. Amethod of operating a steam turbine system, the method comprising:uncoupling a second low pressure steam turbine from a first low pressuresteam turbine using a clutch, the uncoupling being in response to thefirst and second low pressure steam turbine attaining a predeterminedlow part load.
 14. The method of claim 13, wherein the first lowpressure steam turbine includes a first shaft and the second lowpressure turbine includes a second shaft, and wherein the first shaftand the second shaft are capable of coupling and uncoupling via aclutch.
 15. The method of claim 13, further comprising: preventing flowof a working fluid to the second low pressure steam turbine using avalve, the preventing being in response to the first and second lowpressure steam turbine attaining a predetermined low part load.
 16. Themethod of claim 15, further comprising performing the preventing and theuncoupling substantially simultaneously.
 17. The method of claim 15,further comprising controlling the preventing and the uncoupling using acontroller.
 18. The method of claim 17, wherein the controller includesan electromechanical device.